The embodiments described herein relate to a semiconductor memory device, and more particularly, relate to a flash memory device having a three-dimensional structure and a method of programming the same.
Semiconductor memory devices include volatile memories, such as dynamic random access memory (DRAM), static random-access memory (SRAM), and the like, and nonvolatile memories, such as electrically erasable programmable read-only memory (EEPROM), ferroelectric random access memory (FRAM), phase-change random access memory (PRAM), magnetoresistive random access memory (MRAM), flash memory, and the like. A volatile memory loses stored data when powered off, while a nonvolatile memory retains stored data even after powering off. Advantages of flash memory devices include high programming speed, low power consumption, mass storage capacity, and the like. For this reason, flash memory devices are widely used as storage mediums for various computer systems.
The degree of integration of flash memory has generally increased to provide excellent performance and price competitiveness. However, conventional two-dimensional flash memory is limited in the extent to which the degree of integration may increase, e.g., due to the fabrication processes. Three-dimensional flash memory may be developed to overcome such limitations.
Although a three-dimensional structure generally increases the degree of integration, it may also reduce the data reliability, for example, due to the coupling caused by interference between cells or due to program disturbance caused during programming. In particular, when two or more bits of data are stored in one memory cell, the reliability of the data may be reduced.